1. Field of the Invention
The present invention relates to an adaptive reclosing method, in particular, an adaptive reclosing method using a variable dead time control in a power transmission line, which is used to remove faults by means of a circuit breaker being operated by a protective relay and to reclose the circuit breaker after the dead time when the faults are occurred in the power transmission line, thereby automatically recovering the prompt power transmission line network and maintaining the reliability of supply of the power transmission system.
2. Description of the Related Art
Briefly described are theories relating to a reclosing operation, a dead time, and a second arc for re-transmitting the electric power to recover the power transmission line network and to remove faults by operating the circuit breaker when the faults are occurred in the power transmission line, in reference to FIG. 3.
Most of faults occurred in the power transmission line are the arc faults by a flash of lightning, and the permanent faults are less than 10% of the whole faults. The protective system of the power transmission line controls to re-transmit electric power in a short time by installing an automatic reclosing relay and a fault-detecting relay and cut off on occurring the fault, and applying a circuit breaker again if the arc is de-ionized, thereby providing the effects of maintaining the safety and stability of the system and the reliability of supply and increasing the installation utility rate.
FIG. 3 is a flow chart illustrating, by time, the operation of the protective relay, the circuit breaker and the reclosing relay which are related to the reclosing operation in the terminal of the power transmission line. The circuit breaker is started by the operation of the protective relay, and the reclosing relay reclose the circuit breaker by instruction as waiting until the second arc is extinguished after being of the dead time by the circuit breaker trip.
The reclosing time means the total time from the point that the fault is occurred to that both circuit breakers are closed by reclosing.
The dead time means the interval from the dead time after the circuit breaker trip to the time that the ionized air is de-ionized; the insulation of the air is recovered; and the circuit breaker contacts is remaking to transmit electric power. Generally, to reduce the dead time and to speed up the remaking time are advantageous in improving the stability and safety of the system. However, in the event that the remaking time is too fast, it is required to check whether the arc extinction is complete since the arc may be re-ignited when the voltage is applied. The minimum dead time as experimentally required is calculated in the following formula 1.   t  =      10.5    +                  kV        34.5            ⁢              xe2x80x83            [      cycles      ]      
Faults in the power transmission system are classified by two types, a first arc and a second arc. After the fault is occurred in the system, the fault before being removed by the circuit breaker is called the xe2x80x98first arcxe2x80x99. Before the fault is removed by the circuit breaker trip, the fault waveform is indicated as a very big fault current. Although the first arc is removed when the relay detects and the circuit breaker is tripped, a continuous arc constantly flows through the fault point by the capacitive coupling between the fault phase and the normal phase. This is called as the xe2x80x98second arcxe2x80x99. As the second arc is generated at a high temperature in the gas ionized by the first arc, the second arc is not continuously transferred for a long time. Thus, the second arc is finally and naturally extinguished depending on the second arc current, the re-igniting voltage and the length of the arc.
FIG. 1 is a reclosing circuit of the Korean 345 kV power transmission line according to the related art.
As illustrated in FIG. 1, since it needs to wait until the arc at the fault point is de-ionized and the insulation is recovered before the reclosing is shot, the shot of the reclosing is delayed as much as the reclosing time. Here, the reclosing is delayed as much as the dead time determined by the timer circuit, and in the 345 kV power transmission line, a single-phase reclosing being 48 cycle and a triple-phases reclosing being 24 cycles are usually fixed.
FIG. 2 is a reclosing device of a variable dead time as a result of evaluating a transient safety in the related art. As illustrated in FIG. 2, the device receives the information of the power transmission system when the fault occurs, evaluates using the Artificial Neural Network (ANN), and controls the dead time depending on the results. However, the existing arts have a drawback that the breaking duty (fixed dead time) of the existing reclosing scheme is not adaptive or it includes a possibility of error in operation due to delay in eliminating the second arc generated when the fault occurs as the transmission voltage of 765 kv is elevated to cope with the increased demand for electric power.
Further, since the fixed breaking duty in the existing arts is usually operated depending on the fixed dead time, even if the reclosing can be operated with high speed, the reclosing is delayed and the problem of decreasing the reliability on supply is caused.
It is difficult to realize the reclosing technique using the ANN by hardware; it is necessary to further study a way to reduce the learning error of the ANN; and the reclosing technique can be applied, in parts, for a low speed reclosing only because of the evaluation speed problem.
In order to solve the problems of the related arts as indicated above, it is, therefore, an object of the present invention to provide an adaptive reclosing method using a variable dead time control in a power transmission line, in which if a fault occurs due to a sharp increase of the transmission capacity in the 765 kV electric power supply system, it is extended to another faults of cutting a route of the power transmission line, and therefore this fatally affects the maintenance of safety and stability of the system; and an adaptively reclosing technique is performed depending on dead time different each fault by controlling the variable dead time after analyzing the voltage waveform of the relaying point and determining whether the second arc is extinguished and as the result, variably determining the dead time, even if not determining the dead time as a fixed time to prevent the loss in the power transmission system due to the inadaptable reclosing by fixing and setting dead time which is different every fault.
To achieve the above object, there is provided an adaptive reclosing method using a variable dead time control in a power transmission line of a power transmission system including a power transmission line (T/L) and a circuit breaker, the method comprising the steps of: An adaptive reclosing method using a variable dead time control in a power transmission line of a power transmission system including a power transmission line (T/L) and a circuit breaker, the method comprising the steps of: digitalizing by transmitting a voltage waveform of a faulted phase after the circuit breaker trip of the relaying point to 16 bits A/D converter through a potential transformer or a current and voltage transformer in the power transmission line (T/L) in order to provide the power by promptly reclosing an electric power transmission line if a fault occurs in the power transmission line (T/L); eliminating noise by passing the digitalized signals through a low-pass filter; determining the dead time as being variable by analyzing the voltage waveform of the relaying point through applying digital signals eliminating noise to a variable dead time control algorithm provided in a timer and checking whether a second arc at the fault point is extinguished; variably controlling a reclosing relay in correspondence to the dead time; and automatically recovering the power transmission line network by transmitting the control result of the reclosing relay to the circuit breaker of the power transmission system and re-transmitting the electric power by adaptively shutting a real reclosing.
In the present invention, the voltage waveform stored passing through a 16 bit A/D converter through a potential transformer (PT) or a current and voltage transformer (CVT) of the power transmission line (T/L) is passed through a low-pass filter (butterworth secondary filter) designed for anti-aliasing and to remove harmonic wave components.
Analyzing the voltage waveform of the relaying point which is low-pass filtered and tracking and monitoring a effective value of the voltage waveform at real-time, if a time (point of time) for the second arc extinction is determined, a variable dead time is determined. In line with the determined variable dead time result, the dead time of the reclosing device is controlled as variable so that another reclosing shot time (adaptive reclosing method) is determined and thus the reclosing is phased in according to various faults.
Since the 765 kV power transmission line is in process of construction, an algorithm inspection is done using the data obtained in the 765 kV real system modeling through the Electromagnetic Transient Program (EMTP), and the variable dead time control technique (algorithm) uses the language such as xe2x80x9cMODELS in the EMTP compiled in Fortranxe2x80x9d to make it easier to embody in hardware.